Several industries utilize conveyor and process belts for transporting loads from one location to another location or for passing loads through successive processing operations. Many of these applications require conveyor belts that are able to maintain cleanliness under various and sometimes harsh conditions. For example, in the food and dairy industries, conveyor belts must provide sanitary surfaces for conveying food and dairy products to minimize the potential for contaminating these products. To meet this need, conveyor belt surfaces are often formed of materials, for example thermoplastic materials, that do not become easily contaminated when contacted with food or dairy products on the conveyor belt surface. To provide additional tensile strength, light to medium duty conveyor belts used in these applications are typically formed in a plurality of plies, including one or more fabric layers sandwiched between thermoplastic or rubber layers. Thus, in the food product industry, for example, the conveying surface may be formed of a thermoplastic material that does not easily absorb liquid from conveyed food, while the carcass may be formed from a woven fabric to provide strength to the conveyor belt. In addition, in the food product industry and other industries, belts with uniform thicknesses and smooth continuous surfaces have greater strength, produce less wear on a conveyor system, and operate using smaller rollers than belts with nonuniform thicknesses or noncontinuous surfaces.
During installation and maintenance of conveyor belts, the ends of one or more conveyor belts often must be joined together. While several existing methods and tools are capable of joining belt ends together, such as using adhesive or mechanical fasteners to adjoin the belt ends, vulcanized splicing is often the preferred method of joining the ends of conveyor belts, including light to medium duty polyvinyl chloride (PVC., polyurethane, and polyester belts, because it generally provides a more uniform and continuous joint and surface than other methods.
Vulcanized splicing typically includes preparing the ends of one or more belts for splicing in a generally overlapping or intermeshing pattern, positioning the prepared belt ends together in a generally end-to-end orientation between a pair of heated plates, and subjecting the belt ends to specific temperatures and pressures applied by one or both of the plates for a specific amount of time to cause the plastic material in the belt ends to melt or soften and flow together. Upon subsequently cooling the belt ends and releasing the pressure therefrom, the plastic will re-harden, fusing the material of the two belt ends to join the belt ends together. A high quality vulcanized splice will have a thickness that is close to the original thickness of the conveyor belts and a surface that is seamless and continuous between the splice area and the adjacent areas of the belts, without any weakened portions. A poor splice can result in an area of the splice that is thinner than the rest of the belt or an area that contains weakened material from overheating or scorching of the material or incomplete fusion between the materials of the two belt ends. Poor splices can also result in noticeable surface discontinuities, including, for example, recesses extending across the width of the belt. A splice of poor quality may become a weak portion of the belt, prone to subsequent failure. In addition, a poor splice may create surfaces discontinuities that may increase the likelihood of contamination by food products or other types of products and generally degrade the appearance of the conveyor belt to customers. Typical types of splices that may be made with a vulcanized splice press apparatus include finger-over-finger splices, standard finger splices, lapping splices and step joints, among others.
Vulcanized splices of conveyor belt ends have traditionally been formed using stationary or semi-stationary splice presses. These splice presses are relatively heavy, on the order of about 500-1500 lbs, and are either permanently located at a specific facility, or capable of being transported only after disassembling the press and transporting it in parts. These presses generally utilize external pressure or water supplies to provide pressure and coolant for the press during operation. To form a splice, press plates in these types of presses are heated and apply heat and pressure to a splice area of the belt for a predetermined amount of time, all of which depends upon the characteristics of the belts, including the materials from which the conveyor belts are formed, as well as the belt thicknesses.
Melting the ends of a conveyor belt while keeping the belt material adjacent to the melted belt ends cooler is known. Specifically, elevating the temperature of the lateral center or a hot region of the plates positioned at the splicing location on the belts, while maintaining the lateral edges or cool regions of the plates at a relatively lower temperature, causes belt material adjacent to the hot region to melt so that the belt ends can be joined while the material adjacent to the cool zones remains at a cooler temperature and generally remains solid or unmelted to restrict the flow of melted material away from the hot zone. During splicing in these types of presses, pressure is applied to both the hot and cool zones by the plates. Thus the solid belt material adjacent to the hot zone forms a barrier to restrict the flow of material from the hot zone and also forms a spacer for the press plates so that when pressure is applied to the heated belt ends by the press plates, the press plates will not move closer together than the thickness of the belt to form a splice of uniform thickness, which could otherwise squeeze melted belt material from the hot zone. It should be noted that these presses extend lengthwise transversely across the width of the belt so that the longitudinal ends of the belt or belts to be joined together are generally disposed at the lateral center of the belt splicing apparatus.
As is apparent, to achieve a high quality splice with the above-described approach a sufficient temperature gradient across the press plates must be achieved. To this end, U.S. Pat. No. 2,725,091 to Miner et al. describes that cooler areas can be maintained laterally adjacent to a heating platen by circulating coolant liquid through pipes in the cooler area. Other attempts have been made to utilize stainless steel press plates as the pressing surface of the splice press and to generate a temperature gradient across the stainless steel press plates. For example, U.S. Pat. No. 4,430,146 to Johnson describes that a narrow stainless steel sheet can be arranged below a center portion of a wider stainless steel sheet and heated so that the lateral edges of the wider sheet remain cooler than the center portion that is in contacted with the thinner heated sheet. Johnson describes that in this manner, a temperature gradient can be formed against the belt contacting wider stainless steel sheet. One reason stainless steel press plates were used in these presses is because the high stiffness characteristics of stainless steel were believed to withstand the high pressures applied to the press plates during operation without substantially deflecting. Several drawbacks, however, have been identified for each of these techniques. First, running a cooled fluid through lateral adjacent areas as described by Miner et al. significantly increases the complexity of a splice press by requiring coolant hook-ups and piping lines for the coolant. In addition, the splice press requires the use of an external source of hydraulic fluid, which may not be present at many locations where belt splicing is desired, significantly decreasing the usefulness of the splice press.
Further, heating a center portion of a steel press plate, as described by Johnson, has presented several problems. First, heating a center portion of a stainless steel press plate fails to produce adequate cool zones because the heat from the heated center zone rapidly transfers to the adjacent side edges so that the necessary temperature gradient does not form across the press plate. In addition, these stainless steel press plates as well as aluminum press plates have been found to suffer considerable deformation during a splicing operation and become permanently warped when subjected to the high temperatures required to melt and join the conveyor belt ends. Warping of the plates causes the plate surfaces to become uneven, which produces uneven pressure and heating distributions across the splice area during subsequent splicing operations, degrading the quality of the splices formed by the press.
Based on the difficulties for providing adequate cool zones and to avoid permanent deformation of the steel or aluminum platens as described for previous attempts, more recent splice presses have increased the stiffness of the clamping devices by adding a thick, substantially rigid member of heat insulating material in between the steel or aluminum platens and the belt ends. For example, U.S. Pat. No. 5,562,796 to Ertel describes a system that utilizes a narrow metal heating element mounted below a narrow sheet of aluminum. Positioned above the aluminum sheet is a thicker layer of rigid heat resistant phenolic resin, containing silicone and glass fibers. Another commercially available splice press utilizes a similar aluminum plate disposed between a heating element and a belt facing thick, rigid insulating press plate formed of fiberglass or other insulating material for applying heat and pressure to the belt ends. The aluminum layer of this system is used for its heat conducting characteristics to rapidly conduct heat from the heating element to the insulating plate. The insulating members are used in these presses to insulate the flow of heat across the surface of the plate in the lateral directions beyond the edges of aluminum plates therebelow. In this regard, the heating elements and metal portions of the plates in these presses are narrower than the thicker fiberglass plates and positioned laterally centrally below the insulating plate to restrict the flow of heat to the lateral edge portions of the insulating plates, thereby allowing a hot zone to form in the middle portion of the insulating plate with cooler zones being maintained at the lateral edge portions. The application of high heat to the clamping devices, including the platens and fiberglass plates will also typically not cause them to warp to the same extent as the steel or aluminum platens when used alone.
Insulating plate members, however, increase the complexity of the system by requiring the additional thick, substantially rigid layer of insulating material to be mounted over a narrower heated metal component that is adjacent to a heating element. In addition these thick insulating members require the heating elements to reach and maintain relatively higher temperatures during the belt splicing operation, because the insulating effect of the fiberglass tends to keep the maximum amount of heat from the heating element from reaching the overlying belt ends to be melted. In fact, the insulating members themselves substantially increase the amount of mass that must be heated within the system, because the entire thickness of the insulating member must be heated. Because more heat must be generated in order to sufficiently heat the belt ends when insulating members are utilized, this additional heat must also be removed by the system prior to performing a subsequent splice, increasing the cycle time of the press for each belt splicing operation. The fiberglass plates also increase the amount of time required for heating the belt engaging surfaces of the plates and for removing the heat after the splice is formed, decreasing the ability of the user to quickly apply and remove heat from the belt ends for quickly controlling the heat being applied to the belt ends. As a result, it may become more difficult to remove heat from the belt ends. This may detrimentally affect the quality of the splice, because the quality of the splice depends on the heated temperature applied to the belt ends and the amount of time the belt ends are exposed to the heated temperature. Thus, the ability to quickly remove the heat source from the belt ends to regulate the heated temperature is important to the resulting quality of the splice. Cooling the additional heated mass also increases the cycle time of the press before the press reaches a low enough temperature to perform a subsequent splice.
As mentioned previously, stainless steel press plates would often undergo considerable deformation upon heating to a high operation temperature, e.g. 200° C., and become permanently warped. Warping of the plates causes the plate surfaces to become uneven which produces uneven pressure and heating distributions across the splice area during subsequent splicing operations, degrading the quality of the splices formed by the press. Initially, it is believed the plates on these presses were made thicker in an attempt to reduce the amount of operational deflection and permanent deformation that the plates underwent (see e.g. U.S. Pat. No. 4,193,341 to Clements et al. Other presses, such as described by U.S. Pat. No. 6,228,200 to Willis et al., have used support rods and large plate sidewalls to restrict or control operational deflection and permanent warping of the metal plates. However, these approaches require additional strengthening materials that increase the weight of the press, thereby negatively affecting the portability of the press.
The thick, rigid insulating members that have been adopted more recently for being positioned between metal platens and the belt ends are also utilized as a structural member to restrict deflection of the platen by increasing the stiffness of the press surface. In addition, these thick, rigid insulating members do not experience as much permanent deformation as do stainless steel press plates. However, for the reasons described previously, these thick, rigid insulating members create several disadvantages, including increasing the amount of mass that is heated in the system and decreasing the amount of control that an operator has over the quickly adjusting the heat being applied to the belt ends.
As mentioned previously, traditional splice presses have included large stationary presses that are not intended to be transported between facilities other than to be disassembled and transported in pieces. Stationary splice presses are not useful for splicing conveyor belts in all situations. For example, in some instances of repair or installation of a conveyor belt, it may be necessary to form a splice between two belt ends in situ, with the belt left installed on the conveyor system. In addition, in facilities where it would be impractical to include a stationary splice press, it is still often desirable to repair belts at the facility rather than having to ship the belt off-site, which can cause significant expense and unnecessary downtime of operations where the belt is employed. However, these stationary splice presses are typically bulky and heavy and are difficult to transport to a specific site without expending considerable time disassembling, moving, and reassembling the press to the new location.
The traditional splice presses also typically utilize pneumatic or hydraulic fluid for cooling the splice press after performing a splice. More particularly, the heat generated by the heating elements in these presses for applying heat to the belt ends typically must be removed after performing a splice and prior to a subsequent splice, because the entire press may become hot if it is not cooled between splice operations. In addition, the platens should be cooled to a sufficient extent prior to a subsequent splice so that residual heat in the press plates does not cause uneven heat distribution to the belt ends during a subsequent splice, or modify the time heat is applied to the belt ends, since the starting temperature of the platens is higher, resulting in a splice of poor quality. To cool the apparatus, these presses are often connected with tubing to pneumatic or hydraulic supplies to circulate fluid or air from the pneumatic or hydraulic supply through the press to cool the press. However, requiring tubing lines and adapters for being connected to external supplies increases the complexity of the system and further reduces the ability to transport the press from facility to facility due to additional equipment that must be transported with the press and the need to use the press in a location that provides the necessary external supplies.
Attempts to address these problems have been largely unsuccessful. For example, attempts to make splice presses more compact so they can be transported from facility to facility have not considerably reduced the burden in transporting the presses other than to reduce the size of the equipment. Like traditional stationary splice presses, these types of presses are inconvenient for transporting between facilities and require the operator to transport additional equipment with the press and only allow the splice press to be used at certain facilities and at specific locations within the facility providing necessary external supplies. For example, one commercially available splice press requires an operator to transport attachment hoses for running cooling fluid from a fluid source within the facility to the press to cool the press after performing a splice. An additional hookup is required to supply compressed air from a pneumatic source to an inflatable pressure device in the splice press. Similarly, these types of presses either require the operator to use the press with a specific power source or to transport an additional external bulky transformer with the press. External controllers are also required for controlling the temperature applied to the belt ends by the press plates in these presses. For all of these reasons, these more compact splice presses do not provide adequate transportability of the splice press because they require a large number of external components to be transported with the press. Further, they greatly limit the locations at which the press can be used to areas where appropriate power supplies and pneumatic and/or hydraulic supplies are available.
Attempts to remove these external components and the need for external supplies have also proved unsuccessful. To avoid the need to connect hoses to external pneumatic or hydraulic supplies, other mobile presses, for example the press described in U.S. Pat. No. 4,430,146 to Johnson allows the press to passively cool by ambient air. This method, however, decreases the control the user has over the temperature of the press plates and the amount of time the belt ends remain heated after the heating element is turned off, which can degrade the quality of splices formed between belts with materials that are sensitive to temperatures and times. Moreover, as mentioned earlier, passive cooling increases the amount of time that a user must wait until the press reaches a sufficiently low temperature prior to performing a subsequent splice with the press. This delay between splices can be problematic, particularly for belt repair operators who bring these presses from facility to facility and often perform multiple splices at a particular facility, because they must wait to perform subsequent splices, reducing their efficiency.
A further problem with current splice presses is the tendency for the hot press plates to apply excessive heat to the outer surfaces of the conveyor belt before the interior or core belt material is sufficiently melted to join the belt ends, resulting in scorching of the conveyor belt surfaces. Current splice presses typically allow a user to select a melt temperature and melt time for a conveyor belt, using an external controller as described above. The controller subsequently performs a splice operation during which the plates reach the melt temperature and are maintained at the melt temperature for the duration of the melt time. However, in many situations, engaging the press plates against the belt surfaces at a temperature sufficient to melt the belt material and for a time sufficient to melt the material of the entire belt thickness so that the belt ends can be joined together often causes the belt surfaces to become overheated and scorched, degrading the strength and appearance of the splice.
Each of the problems associated with current splice presses reduces the overall quality of splices formed by the splice press and the mobility of the portable splice press, by increasing its weight, limiting the locations in which it may be used, and increasing the amount additional external equipment that must be transported with the press.